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'Complete' Brake Job Not a Must

November 16, 1989|RALPH VARTABEDIAN | TIMES STAFF WRITER

Question: Can you please describe what would normally be involved in a complete brake job and when you need it? I'm not sure what repacking the wheel bearings means or resurfacing the rotors and drums or rebuilding the calipers. But all these technical terms are thrown at me.--J.Y.

Answer: Along with mufflers, tuneups and oil changes, brake jobs are one of the most regular services your car will need. In terms of safety, not to mention avoiding additional costly repairs, brakes simply cannot be ignored.

You can determine when you need a brake job by having your car regularly serviced according to instructions in your owner's manual. During these periodic inspections, every 10,000 to 15,000 miles, you will get a report that describes the percentage of wear on the brakes. When the brakes are 80% or 90% worn, then it's time to have a brake job.

General Motors has gone a step further and installed brake wear indicators on their new cars. These brakes screech when they are nearing the end of their useful life, letting the motorist know it's time to head for a garage.

A great deal of the work done under the so-called complete brake job packages sold by garages, dealerships and tire stores is utterly unnecessary and goes against some manufacturers' recommendations. It is sold at high cost because people want to have a "complete job" even though they probably need much less than that.

In general, disks should not be resurfaced and drums should not be turned unless they have been scored, warped or damaged. Many shops want to machine drums and disks at every brake job. Not only is this a needless expense, but it may prematurely wear out those parts and they will have to be replaced.

In addition, calipers and wheel cylinders should not be rebuilt unless they show signs of damage, corrosion or leakage. Of course, the chances of needing the service becomes greater as the car gets older; by the time it has 60,000 or 80,000 or 120,000 miles it may well need this service.

General Motors, for example, recommends only that mechanics inspect the disks and drums, calipers and wheel cylinders and other parts during a brake job. If those systems are in good condition, the mechanic need only replace the brake shoes and brake pads. Nissan makes the same recommendation.

Motorists should have a basic understanding how brakes work and what the different parts do.

There are two basic types of brake systems: drums and disks. In drum brakes, which are used mostly on the rear wheels, a heavy cast-iron drum a bit larger than a gelatin mold is mounted on the wheel. Two curved brake shoes lined with friction material are inserted inside the drum. When you press your brake pedal, hydraulic pressure travels through a tube to the brakes. The pressure causes a piston in a part called a wheel cylinder to press the shoe against the drum, creating friction and stopping the car.

In disk brakes, a disk about the size of a dinner plate is mounted on the wheel and two pads are positioned on either side. The hydraulic pressure causes a piston inside a part called a caliper to squeeze the pads against the disk, which creates the stopping friction.

Over time, the surface of a disk or drum can become irregular. And if the friction material wears out, the metal backing of the shoe or pad can gouge the surface of the drum or disk. If this happens, the disk or drum can be ruined.

In calipers and brake cylinders, the extreme hydraulic pressures can cause seals to eventually leak fluid. These parts can be either replaced or rebuilt.

Finally, many garages also "repack" the front-wheel bearings on which the front wheels ride. Your car may not need this service, though it won't hurt anything and should not cost much. The mechanic removes the bearings, cleans them in a solvent, dries them and then lubricates them with a heavy grease.

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